Chase Stadium in San Francisco opened in 2019 as a cornerstone of the transformation of the Mission Bay Neighborhood (a former industrial zone) into a thriving entertainment and transportation hub. Home to the Golden State Warriors of the NBA, the stadium and the surrounding commercial and retail buildings were built on what used to be a shallow inlet of San Francisco Bay. The site was filled in since the Gold Rush days with excavated material from all over San Francisco, including rubble and fire debris from the 1906 earthquake, and even garbage! The geotechnical and environmental challenges of building at this site were many, to say the least.
There is an excellent article about the project in the December issue of Civil Engineering Magazine which included a section on the geotechnical challenges. There was also a follow-on article by members of the Langan Engineering and Environmental Services Inc. team, who were responsible for the geotechnical and environmental engineering for the site, that dives deeper into the technical challenges. The articles are well worth the read. Here are a few points that stood out to me:
- Extensive geotechnical explorations found evidence of a “mud wave” where reclamation fill was placed too quickly over the very soft marine clay “bay mud” causing a bearing capacity failure of the native clay.
- Site segmented into 8 zones with different geotechnical recommendations for soil bearing etc.
- Being close to the bay, shallow groundwater (6 to 12 feet deep) required cutoff walls and dewatering requiring extensive groundwater testing and modeling.
- Close proximity to San Andreas and Hayward faults.
- A below-grade practice facility meant that deep foundations were required as “hold-downs” to ensure the slabs do not float upward. Uplift pressures as much as 800 psf were accounted for.
- Portions of the reclamation fill contained boulders with naturally occurring asbestos. It also contained contaminants including chromium, lead, nickel, and hydrocarbons requiring proper cleanup and disposal of hazardous material.
- Deep foundations were needed because of the weak bay mud as well as high seismic loading. A combination of 24 in. auger cast piles and 36 or 48 in. diameter drilled shafts was used.
- A total of 1,300 deep-foundation elements installed.
- The tight schedule required four foundation rigs and three shoring rigs operating concurrently.
- Mortenson|Clark JV was the general contractor, Malcolm Drilling was the foundation contractor and Condon-Johnson & Associates was the shoring contractor. Magnusson Klemencic Associates was the structural engineer. Shoring and foundation inspection by Divis Consulting. As noted, Langan provided geotechnical and environmental engineering.